A. I
came across a short list of downtown filming notifications (designed to
warn downtown residents about filming that might affect their lives), and
there were three Dexter filmings listed: one on Santa Fe (Tito's
Bar), and two nearby on 6th Street (this location and the supply
store).

Once
I came across locations that looked like they might be in the warehouse
district, I used Google StreetView (see above) to look at both addresses,
and was able to match up this location with the scene.